The present invention relates generally to vehicle compartments, and more specifically to supplying vehicle compartments (e.g., a fuel tank) with an inert gas to prevent the compartments from combusting.
It is well known to supply an inert gas, such as nitrogen-enriched air (NEA), to the ullages (i.e., the portion of a tank above the liquid) of an aircraft fuel tank to prevent the tank from combusting. In the past, storage tanks on the aircraft have been charged with compressed NEA from an external source to supply the fuel tanks during flight. Currently, some aircraft include on-board inert gas generating systems (OBIGGS) for generating the NEA on-board the aircraft from conditioned engine bleed air. However, some OBIGGS may not generate the NEA at a flow rate sufficient to ensure the gas above the fuel in the tank is incombustible during some operating conditions of the aircraft. This may be particularly true for transport aircraft with large fuel tanks. The OBIGGS therefore compresses and stores the excess NEA it generates during periods of low demand in storage tanks on the aircraft for supplying the fuel tanks later during flight. The stored NEA is regulated to a lower pressure and delivered to the fuel tanks. When the aircraft is being refueled, fresh fuel flows through scrubbers to remove dissolved oxygen that would otherwise escape from the fuel and fill the ullages.
Because the OBIGGS may not generate the NEA fast enough to fully charge the system during short flights, flight crews may be required to project usage of NEA and charge the storage tanks accordingly before flight. Additionally, the stored NEA is gradually consumed as the ullage temperature changes while the aircraft is parked. If the aircraft (and therefore the OBIGGS) is not operated daily, it may take several hours to supply the fuel tanks with sufficient NEA, making it difficult to quickly prepare the aircraft for flight. The storage compressors and tanks may need to be replaced periodically and can be difficult to remove due to their location, size, and weight. Furthermore, potential leakage from the storage tanks and associated components may require maintenance personal to sample an oxygen level adjacent the OBIGGS before accessing the OBIGGS for maintenance. Even small leaks from the storage tanks and associated components may prevent the storage tanks from storing enough NEA to sufficiently supply the fuel tank so the gas above the fuel is incombustible during descent of the aircraft.